include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/abis_nm.h b/include/osmocom/gsm/abis_nm.h
index 86b97eb..bc13ffe 100644
--- a/include/osmocom/gsm/abis_nm.h
+++ b/include/osmocom/gsm/abis_nm.h
@@ -1,5 +1,4 @@
-#ifndef _OSMO_GSM_ABIS_NM_H
-#define _OSMO_GSM_ABIS_NM_H
+#pragma once
 
 /*! \defgroup oml A-bis OML
  *  @{
@@ -47,5 +46,3 @@
 enum gsm_phys_chan_config abis_nm_pchan4chcomb(uint8_t chcomb);
 
 /*! @} */
-
-#endif /* _OSMO_GSM_ABIS_NM_H */